Peroxygen bleaching agents are useful only when the available oxygen content in the laundry wash water can be controlled. Thus, agents which provide a high, stable alkalinity are employed. U.S. Pat. No. 3,697,217 teaches the use of sodium carbonate, sodium silicate, trisodium phosphate, or a mixture thereof as an "alkalinity booster" in a bleaching composition containing sodium perborate and/or sodium monopersulfate. Similarly, U.S. Pat. No. 3,894,960 teaches the building of the sodium perborate or percarbonate by admixing with a separately prepared high sodium silicate detergent powder which also may contain an amide type activator.
Although the alkali silicates operate somewhat to stabilize the available oxygen content, their presence also appears to cause accelerated caking on storage. It appears from physical inspection of the manner in which the caking first manifests itself that the hydrous alkaline polysilicate and the percarbonate tend to produce on contact a lower melting eutectic.
German Pat. No. 870,092 teaches the use of a fumed silica to stabilize percarbonate. The process of this patent has been severely criticized in U.S. Pat. No. 3,951,838. The latter patent contends that in the German process, the silica particles have only a partially hydrated structure and are not dispersible in water to yield low viscosity, high concentration sols without the application of sufficiently high shear forces to disaggregate the particles. The German process is further criticized as being time consuming, cumbersome and costly, involving the application of excessively high quantities of energy to mechanically initiate the necessary chemical reaction to achieve dispersion.
U.S. Pat. No. 3,915,838 describes the preparation of a stabilized sodium percarbonate by the use of an aqueous sol containing 3 to 8 percent of silica having a maximum particle size of 0.1 micron. The silica is prepared by deionizing a solution of a water soluble silicate to a pH of 3 to 10 in order to deposit on the percarbonate particles from 1 to 10 percent by weight of silica based on the weight of the percarbonate. In practice this patented process requires the preparation of freshly prepared silica sols which are of necessity applied to the dry percarbonate particles as an aqueous suspension and therefore requires subsequent drying in order to arrive at a dry, free flowing product.
It is the primary object of the present invention to provide peroxygen bleaching and laundering compositions having excellent stability.
A further object of the present invention is to provide a means whereby the caking of dry granular household laundry bleaches is prevented and the flowability enhanced.
These and other objects will be apparent from the description which follows.